CS 61B: Lecture 1
Wednesday, January 18, 2012
Prof. Jonathan Shewchuk, jrs@cory.eecs
Email to prof & all TAs at once (preferred): cs61b@cory.eecs
Today's reading: Sierra & Bates, pp. 1-9, 18-19, 84.
Handout: Course Overview (also available from CS 61B Web page)
Also, read the CS 61B Web page as soon as possible!
>>> http://www.cs.berkeley.edu/~jrs/61b <<<
YOU are responsible for keeping up with the readings and assignments. I won't
always remind you. The course newsgroup is required reading: ucb.class.cs61b
Labs
----
Labs (in 273 and 275 Soda) start Monday. Discussion sections start next Wed.
You must attend your scheduled lab (as assigned by Telebears) to:
1) get on the class list so we can give you a grade, and
2) get an account (needed for Lab 1 and Homework 1).
You may only attend the lab in which you are officially enrolled. If you are
not enrolled in a lab (on the waiting list or in concurrent enrollment), you
must attend a lab that has space (show up and ask the TA if there's room for
you).
You will not be enrolled in the course until you are enrolled in a lab. If
you're on the waiting list and the lab you want is full, you can change to one
that isn't, or you can stay on the waitlist and hope somebody drops.
If you're not yet enrolled in a lab, just keep going to them until you find one
that has room for you (that week). Once you get enrolled in a lab, though, you
must always attend the one you're enrolled in.
Prerequisites
-------------
Ideally, you have taken CS 61A or E 7, or at least you're taking one of them
this semester. If not, you might get away with it, but if you have not
mastered recursion, expect to have a very hard time in this class. If you've
taken a data structures course before, you might be able to skip CS 61B. See
the Course Overview and Brian Harvey (781 Soda) for details.
Textbooks
---------
Kathy Sierra and Bert Bates, Head First Java, Second Edition, O'Reilly, 2005.
ISBN # 0-596-00920-8.
Michael T. Goodrich and Roberto Tamassia, Data Structures and Algorithms in
Java, Fifth Edition, John Wiley & Sons, 2010. ISBN # 0-470-38326-7.
(The first/third/fourth edition is just as good, but not the second.)
We will use Sierra/Bates for the first month. Lay your hands on a copy as soon
as possible.
Buy the CS 61B class reader at Vick Copy, 1879 Euclid. The bulk of the reader
is old CS 61B exams, which will not be provided online. The front of the
reader is stuff you'll want to have handy when you're in lab, hacking.
Grading
-------
10 pts Labs There are 200 points total you can earn in this course,
20 pts Homeworks broken down at left. 185+ points is an A+, 175-184 is
70 pts Projects an A, and so on down to D- (75-84). There is NO CURVE.
25 pts Midterm I Late homeworks and labs will NOT be accepted, period.
25 pts Midterm II Late projects are penalized 1% of your score for every
50 pts Final Exam two hours by which you miss the deadline.
-------
200 pts
There will be three projects, worth 20, 30, and 20 points respectively. You
will do the first project individually, and the last two as part of a group of
two or three students. You may not work alone on the last two projects.
All homeworks and projects will be turned in electronically.
Cheating
--------
...will be reported to the Office of Student Conduct.
1) "No Code Rule": Never have a copy of someone else's program in your
possession and never give your program to someone else.
2) Discussing an assignment without sharing any code is generally okay.
Helping someone to interpret a compiler error message is an example of
permissible collaboration. However, if you get a significant idea from
someone, acknowledge them in your assignment.
3) These rules apply to homeworks and projects. No discussion whatsoever in
exams, of course.
4) In group projects, you share code freely within your team, but not between
teams.
Goals of CS 61B
---------------
1) Learning efficient data structures and algorithms that use them.
2) Designing and writing large programs.
3) Understanding and designing data abstraction and interfaces.
4) Learning Java.
THE LANGUAGE OF OBJECT-ORIENTED PROGRAMMING
===========================================
Object: An object is a repository of data. For example, if MyList is a
ShoppingList object, MyList might record...your shopping list.
Class: A class is a type of object. Many objects of the same class might
exist; for instance, MyList and YourList may both be shopping lists.
Method: A procedure or function that operates on an object or a class.
A method is associated with a particular class. For instance, addItem might
be a method that adds an item to any ShoppingList object. Sometimes a method
is associated with a family of classes. For instance, addItem might operate
on any List, of which a ShoppingList is just one type.
Inheritance: A class may inherit properties from a more general class. For
example, the ShoppingList class inherits from the List class the property of
storing a sequence of items.
Polymorphism: The ability to have one method call work on several different
classes of objects, even if those classes need different implementations of
the method call. For example, one line of code might be able to call the
"addItem" method on _every_ kind of List, even though adding an item to a
ShoppingList is completely different from adding an item to a ShoppingCart.
Object-Oriented: Each object knows its own class and which methods manipulate
objects in that class. Each ShoppingList and each ShoppingCart knows which
implementation of addItem applies to it.
In this list, the one thing that truly distinguishes object-oriented languages
from procedural languages (C, Fortran, Basic, Pascal) is polymorphism.
Java
----
Java allows you to store data in variables, but first you must _declare_ them
and specify their _type_.
Scheme: (let ((x 1)) ) Python: x = 1 Java: int x;
x = 1;
This declaration does two things.
(1) It allocates a chunk of memory big enough to store an integer, which
Java calls type "int".
(2) It names the variable (chunk of memory) "x".
Variables are used not just to store numbers, but also to _reference_ objects.
There are two ways to get classes of objects to play with:
(1) Use one defined by somebody else. Java has tons of pre-defined classes
you can use. Many come in the "Java standard library" provided with every
Java compiler.
(2) Define your own.
For example, Java has a built-in class called String.
String myString;
This does _not_ create a String object. Instead, it declares a variable (chunk
of memory) that can store a _reference_ to a String object. I draw it as a
box.
---
myString | | | | a String object
--- ------
Unlike Scheme and Matlab, Java programs must be compiled before you can run
them. _Compilation_ converts your written code to a machine-readable bytecode.
The advantage is a faster program than one written in Scheme. The disadvantage
is that you have to wait for it to compile.
Scheme Java
------ ----
Scheme program (.scm) Java program (.java)
| |
| eval | javac
v v
Answer .class files
|
| java
v
Answer
Postscript: Anatomy of a Small Java Program (for discussion section)
--------------------------------------------
Assume the following code is in a file called HelloWorld.java:
class HelloWorld {
public static void main (String[] args) {
System.out.println("Hello, world");
}
}
The classes are "HelloWorld", "String", and "System".
The objects are "args", "System.out", and the string "Hello, world".
(Actually, the first two of these are _references_ to objects.)
The methods are "main" and "println". The println method prints its parameter,
and the main method prints the string "Hello, world".
You don't have the knowledge to completely understand this code yet, but don't
worry about it. We'll take the first two lines on faith as the standard way to
start a Java program. They'll become clear in the coming weeks.
Let's look at the innermost line first; it does all the action. "out"
references an object whose class is PrintStream. A PrintStream is a path by
which characters can be output by a program. The characters that are sent
through "out" find their way to your computer screen.
System is a class which happens to contain the variable out (among many other
variables). We have to write "System.out" to address the output stream,
because other classes might have variables called "out" too, with their own
meanings.
"println" is a method (procedure) of the class PrintStream. Hence, we can
invoke "println" from any PrintStream object, including System.out. "println"
takes one parameter, which can be a string.
"main" is a method in the "HelloWorld" class. The HelloWorld class knows how
to do the "main" operation, just like the PrintStream class knows how to do the
"println" operation.
------------------------
------------------ ---------------------- | |
| | | | | |
| --- | | println (method) | | |
| out |.+-----+-->| | | |
| --- | | | | main (method) |
--System (class)-- --An object of class-- | |
PrintStream | |
---HelloWorld (class)---
The classes System and PrintStream are all automatically provided for you by
any Java compiler. Somebody has programmed them for you, so that you don't
have to figure out for yourself how to send characters to the terminal.